Synchronous motor



Dec. 23, 1952 K. L. HANSEN 2,623,201

SYNCHRONOUS MOTOR Filed Aug. 5, 1950 s Sheets-Sheet 1 1 A0/d577i645 l i A? AZ v fl/Z INVEN TOR. M 13 Z. 351151 1? 2 m WWW; filth/way Dec. 23, 1952 K. L. HANSEN 2,623,201

SYNCHRONOUS MOTOR Filed Aug. 5, 1950 3 Sheets-Sheet 3 IN V EN TOR.

Patented Dec. 23, 1952 UNIT-ED E1 2,623,201lf SYNGHRJGNOUS' MOTUR Klaus .Ll Hansen, M-il waukemwwisl nppliatidnnu use's, 1950 f-Srittl' Nb 177 1928 6' Claims.i (Cl. 3-18fl186)' This invention relates to synehronous motorsz Objects "of thisi invention are to provide arselfst'arting and-' self compeiisatirig synchronous" mo tor whose charaeteristics can be utilized tri lionre'ct eertaindefects now existing in distrib11'tion'=, generating-andtransforming-equipment'g while at the same time providing 5- a highly movel fsyri chronous motor having characteristics irectly 'adapting themotor for -use competition-with the conventional type of induction motors.

It has-long been recognized that reactive cur rents circulating in power circuits and windings of machines constitute a tremendous waste= of energy. Furthermorethe=capacityofgenerating; transforming and transmitting equipment must besufiicient to-'handle'-the parasitic -reactiye' load imaddition "to=the useful'-power""'load. wre all wattless currents eliminated; it is" conservatively estimated" that 25- per-cent{-m'ore 1dad'could} be generated and tr ans'm'itt'ed.- with"- present -'-equip ment;

Recognition of "the-appalling waste engendered by therea'ctivekfi v: a. in pow'er icircuits has-1w to installation of capacitors. At" best; however;

it"is*only apm'aikeshi ft 'solutiorr; Capa-citors'ud not "provide forautomatic neutralization of I the reactive'-component"witni'load. To achieve even approximate adjustmentto ohanging'lo'ad-eondF tions requires wanemborate system" of switches Furthermore; correction orpower factor at -onepointof a'plaritiayoutdoes'noteliminat tasterurwattiess currents in thepiafiit circuits: Low poweriactonsliould*bvcorrectd at"the"sour'ce:=

However, in spite of' its'relatively -high power factor, the general purpose induction motor-com stitute's" by f-ar'i'thegreatest*-source :01 wattless currents in powerlihes' because'of the trerm'e'm'ious amount of connected'ioau; The general purpose induction motor has to be notonly tolerated-but compensated for by other"-'means? since it 'is" in such extensiveuser Furtherifobj e'cts' are to; PidVidBW synchronous rrrotorwhich "is relativelyinexpensive to :makvas compared with "the'cost of theiconventi on'al typ e of'synchronous motor Iand"whiohmay be-mad'e at mum 1ess,."-co'st'" than" such conventional chronous "mot-or and which further-comm madeat a." cost competitive with' that"'ofrthe conven 2 synchronous;:motorc-whemoperating at synchronous spe'edw Further fohj ectssare 'atoaprovi'de' a. vself-compel! sating;'self'-starting synchronousrmotorwhicnhas:

unity-v power" factor ror adefinitely .2 leading power:

factor atiallloads .whi'chfineedsiionly substantially the samestarting equipment as ari'induction .11m tori and in :whi'ch" the..:design1 andlzconstruction- 01; the. asynchronous. motor is; much- 1 simplified vibes cause-smaill air gaps can berempioyedz Embodiments a: of ithe iinvention Jare sh-own :in the accompanying; drawings; in -Which I Figuretl is audi-agrammatieilview showingi one. formthat: theinvention imaytake where the fieldi of the synchronous motor is supplied tnrongnca synchronous rectifienfrom -a transformershaving bothzseriesz and ipotentieil primar y windings-:

Figure" 2 is a diagrammatie= and rragmentar ydetail showing (a portioniof -the transformer: used with the-equipmenttof Figure 1.

Figures isza .ve'ctor: dia'g iam showi'ng the- -vo1t age induced "in .1 the; secondary lwinding s' of tlie' transformeifi at no I load and with-' increasing loads-.

Figure. 4 is a vie'w' of a furthenfdrm oi thein vention inl which the potential -transformers builttinto the: sta'to'rof; :the synch ronousi motora Figure-A5 is aview-"of a "further-form' of duffe -in vention' which a separate potential and a sepa rateseries transformei supplythe displaced; field coils of thea rotor? Referring to the di awingw par tieiil'arly Fig; ur'es :1, 2::a1'ldif3; where the firstififoi ni of the-m ventioni is illustrated, it" will be seen-than thereference character I indicates"generally asyn chronous motor :and the 'reference character"'2 a particulanform of-transformer 'Ih'esyn'ch-ronous noto'risprovidedwith apolyphasestator winding indicated generally by the reference character 3 which: in the-instance shown; is* three phasee It is -also provided with -asquirrel eagerotor, prefe'i' ably: of ;hi'ghi:resistanoe so tese'cur'e excellent starting ich'araeteristi'cs The rotor athe sm- ChLOHO'LISZ :motor is: 'indicated by- :the reference character :4 f and: isprovided with afield winding 5' andzis' rigidly": connected to a pair of two-sag ment commutatorsrsfiszand It i to lie-motel? that sone segmenti'ot eaehsorstiieammmutators are: connected together as 'indicatd at 8 al id that the othentwosegmentsare connected tab a-1n DOSite .1 sides :of ath' field win din g z 5" flltfiei m me; The-segments oi itheiscommutator and: h eda r eht angles to -eaefi ther as be seen fromi'Figui-e 1. and pairs of brusheeil in bear on the commutators 6 and 1;

The-brushes: 9 i are suppliedfi om the winding 1 I on the stationary: rotor or core member" I2 of the -special transformer 2 and the brushes =1- are supplied fr'om the other secondarywindihg' l3-on the' roto'r -I-2=;" Itis to he noted tliafitl'ie in the number of the commutators 6 and 1.

The primary of the special transformer 2 consists of a polyphase potential primary winding l4 and a polyphase series winding l5. The rotor is stationary and the primary windings are stationary. However, there is an initial adjustment permitted for the rotor l2, whereby it may be rotated to secure the exact phase angle desired for the secondary windings. In addition to this, one or both of the primary windings M or 15 may be adjustable. The series winding 15 has been indicated as adjustable. I

- At this point, attention is directed-to Figure 2 which shows schematically the special transformer Z. The windings II and 13 are diagrammatically indicated and the primary windings l4 and 15 are similarly diagrammatically indicated. The'co'res for the primary windings l4 and 15 are indicated by the reference characters l6 and 11. It is intended, as stated, that the rotor be revolubly adjustable initially and thereafter locked in place so as to secure the exact relation desired between it and the primary windings l4 and I5. Also it is;intended that the primary winding l be rotatably adjustable aboutthe axis of the rotor l2, so that any adjustment desired can be obtained.

1 In Figure 3 the vector diagram of the voltages impressed on the rectifier at no load and at gradually increasing load have been indicated. The line O-Y shows the voltage impressed on the rectifier due to the primary winding [4 and the line OX indicates the voltage impressed on the rectifier due to the primary winding or series winding at no load. The voltage O-Y is the highest voltage that will ever be impressed on the field of the synchronous motor due to the potential winding. The resultant voltage indicated by the line OZ is the vector sum of the voltages O-Y and O--X. The condition shown in full lines and described thus far is under no load conditions. However, as the load increases the increments in the load produces correspondingly increased voltages impressed on the series primary winding I5 as shown, for instance, by the line ,O-X'. The vector sum is now indicated by the line OZ'.

To state this in other words, it is pointed out that at no load the current supplied the motor is small and the rotating magnetic field of the primary 15 of the transformer is weak., The primary [4 of the transformer induces the voltage in the secondary having a predetermined unchanging value. However, at no load the weak rotating field due to the primary l5 induces only a small voltage in the secondary whereas the field current at no load will set up a high counter E. M. F. The voltage induced by the shunt or potential primary [4 encounters a high selfinduction as the secondary passes under the primary l5 and is, therefore, limited to a relatively low value. However, as the current in the primary l5 increases, it reduces this value of selfinduction and, therefore, permits more current to flow through the secondary winding and, therefore, increases the field current of the synchronous motor.

Furthermore, the primary I5 is so placed relatively to the primary 14 that there is an increasing lag in the phase of the resultant voltage in the secondary as the load increases. Thi is necessary to offset the change in relative posi- 4 tion of the segments of the rectifier as the load on the synchronous motor increases due to the increase in the torque angle or distortion angle of the synchronous motor.

Substantially the sameeifect canbe produced by winding a separate secondary 18 directly on the stator itself. The secondary [8 may be two phase, as shown, in order to simplify the constructlon of the rectifier or may have any number of phases depending on the number of commutators employed. This is described in my prior Patent 2,460,006 of January 25, 1949 for Rectifier and Transformer Unit. The stator winding of the synchronous motor is indicated at l9 in Figure 4, the rotor at 20 and the field winding of the rotor at 2|.

In this form of the invention, a separate, special transformer 22 is provided and is a transformer having the series primary winding indicated generally by the reference character 23. The secondary of the transformer 22 is indicated by the reference character-24 and is wound on the stationary rotor 25. The rotor 25, as well as the series primary winding 23, may be adjustable.

The secondaries I8 and 24 are connected in series and to the brushes 2t and 21 of the commutators 28 and 29. These commutators are two segment commutators with a pair of segments connected as indicated at 30 and with the other pair of segments connected to opposite sides of the field winding 2| of the synchronous motor. Obviously, the same vector relation of voltages may be had in this form of the invention as that previously described for the first form and indicated in Figure 3 of the drawings.

It is to be understood that the field winding of the rotor may be a distributed winding or it may be a winding for a rotor having salient poles, though the distributed Winding is preferable. The coils of the distributed winding in order not to have a poor distribution factor are omitted from several slots in the center of the pole as they add very little to the M. M. F. of the D. C. winding. The idle slots can be used to an advantage by placing low resistance, squirrel cage bars in the unused slctsand connecting them by heavy end rings. This does not in any way interfere with the high resistance cage of the rotor.

If desired, the rotor may be geared to the commutators so as to reduce'the number of segments required for the commutators in the event the stator has a large number of poles. In this case, however, suitable slip rings would have to be employed in addition to the commutators.

When the resisting torque varies periodically, the angular velocity of the conventional synchronous motor undergoes periodic alterations which give rise to a tendency to hunt. There is some tendency to hunt in the synchronous motors hereinabove described and illustrated in Figures 1 and 4, but to a lesser degree than conventional synchronous motors and particularly so when non salient poles are employed. However, a different manner of eliminating this tendency to hunt due to periodic variations in .the load with resulting periodic variations in the displacement angle may be accomplished by the means shown in Figure 5.

In the form of the invention shown in Figure 5, separate potential and series transformers are employed. The series transformer is indicated generally by the reference characterv 3| and the potential transformer by the reference character 32. The primary or the series transformer is 111-.

dicated' at i33-l andnth'e': primary or thepotential;

cated at '36; The" synchronous motor-ls provided with two setsofsyn'chronous rectifiers, each set being" connected: as-previously described. One set, namely; that indicated generally by the reference character 31, is supplied from the secondariesr'of the seriestransformer Sl' andsupplies the-field winding 38 ofthe rotor M of the synchronousmotor; The field winding All i suppliedthrou'g'h the commutators' 39 from'the secondaries of the potential transformer 32. These field windings 38 and Mi are electrically at right angles'and thus produce a resultant field composed ofthe two M. M. F. vectorially added. In thisiform of the invention, the potential transformer feeds a relatively light field winding through its rectifier and furnishes the no load excitation. The series transformer feed a heavier fieldwinding through its rectifier. This last mentioned field winding which is displaced 9o electrical degrees from the other field winding furnishes the ampere turnsnecessary to neutralize the increasing magnetification of the stator. It will be'observecl'with increasing load the center of the M. M- F. of the rotor moves through an angle sufficient to offset what would ordinarily be the displacement angle of a synchronous motor.

Inall forms of the invention, a high resistance squirrel cage rotoris provided. As the squirrel cage is not depended on to furnish any appreciable amount of torque in the upper range of the speed torque curve, it is, as stated, of high resistance to increase the starting torque and limit the inrush current. Also it is to be noted that the air gaps in the magnetic circuit may be greatly reduced below that of the conventional synchronous motor.

It will be seen that a novel form of synchronous motor'has been provided by this invention which is self-startingand self-compensating, which has .a high starting torque several times that of the conventional synchronous motor and a' high accelerating torque and an excellent pullin characteristic with automatic smooth transition into synchronism.

The synchronous motor is self-compensating andflwill provide a unity ora definitely leading power factor at all times depending on the adjustment' and design of the machine. Further, it is to be noted that this invention makes it possible to provide a more economical design because smaller air gaps in the magnetic circuit are employed and also it is to be noted that very simple starting equipment, such as used for an ordinary squirrel cage motor may be employed.

Advantagesof this invention become more apparent when the following detailed examination of the conditions existingatstarting, during acceleration, and when pulling into synchronism are made.

Assume that full line voltage is applied at starting, The torque and current are determined mainly by the resistance of the cage during the sta rting *period; At" full frequency' the induced voltage in the D. C. field is high, but the resistance voltage is also high, so the net voltage and culrent are nominal. At starting, the voltage impressed by thetr'an's'formenis tcc-lowrin propore tion to the induced and reactancevoltages to have any appreciable influence.

At standstill thevoltage impressed onthe field by the transformer is of'line frequency. As the motor accelerates, this voltage is converted by the rectifier to slip frequency and thus combines with l the induced voltage to produce -the resultantcurrent. The influence of the impressed =Voltageis inappreciable during the early stages of "accelera tion, but increases in importance. as'the-motor speeds up, especially as "it approaches synchro' nism.

In the conventional synchronous motordthe cage is depended on tobringthe' motorclose-to synchronism before applying the D; C; voltage. Thisrequires *a low resistance cage when the re;-

sisting torque is appreciable and a lowresistance When the-D10;

cage means low starting torque. voltage'is' applied, an alternating torqueof slip frequency is superimposed on the torque develop? ed by the cage.

In order that the motor should synchronize, a torque peak; minus the resisting torque, mustbe 1 sufiicient' to accelerate the inertia load in less than half cycle of" slip frequency. The average.

At synchronism the external voltageimpressedEisautomatically converted to D. C.

It is .tobe noted particularly that this. syn chronous motor is self-compensating.because of a novel means of compensating forthe-torque angle shift. on the one hand, andon the other hand, of

preventing any torque angle shift. Both of these results are accomplished byarranging .tWo magnetic fields at right angles to each otherzwith one of the fields responding to the voltage-impressed onthe motor and. theother responding. to the currentdemanded bythe motor as theloadi comes-on:

In the first two forms of the invention, there.v

is a' phase shift of the rotating magnetic-fieldin the transformer which phase shift corresponds to the torque angle'shift of therotor. Thismaintains commutation at the. segments: of the syn-- chronous rectifier at zero voltage at all loads- In. the last form of theinvention where the rotorhas two fields at right angles electrically to each.

other, there isia' phase shift inthe magnetic field of the-rotor itself correspondinggto ,what'would.

be the torque angle shift of the rotor so that the netresult is no torque. angle shift'and commutaition is maintained at zero. voltage.

In other words, the brushespass over thegaps in their'respective commutatorswhile:thevoltage. curveiis passi-ng through zero' in all. forms ;of the.- invention, and compensation is securedl for all. changesin loads. to thereby maintain. commutae tion at zero voltage.

Compensation is also. secured'in. that: asathe load increases, the field strength increases and thus unity or a definite leading power factor is obtained at all loads depending on the design or: adjustment of: the device.v

Excellent self-starting characteristics are secured by having the cage of high resistance and excellent running characteristics at synchronous speeds are obtained due to the manner in which the field is controlled. To express this in other words, in the first two forms of the invention, the phase angle shift due to changing loads is obtained in the special transformers while in the other form of the invention, the phase angle shift is obtained in the magnetic field of the rotor of the synchronous motor.

Although this invention has been described in considerable detail, it is to be understood that such description is intended as illustrative rather than limiting, as the invention may be variously embodied and is to be interpreted as claimed.

I claim:

1. A self-compensating synchronous motor comprising two elements consisting of a stator and a rotor, one of said elements being provided with a polyphase winding and the other of said elements being provided with field winding means, synchronous rectifier means driven from said rotor and having segments connected to the field winding means and provided with brushes, and transformer means having its secondary connected to said brushes, whereby said commutator and brushes constitute means for supplying direct current to the field winding means when said rotor is at synchronous speed and whereby said rectifier means converts line frequency to the frequency induced in said field winding means during starting and acceleration prior to the time that said rotor attains synchronous speed, said transformer means having a polyphase series and potential primary.

2. A self-compensating synchronous motor comprising two elements consisting of a stator and a rotor, one of said elements being provided with a polyphase winding and the other of said elements being provided with field winding means, synchronous rectifier means driven from said rotor and having segments connected to the field winding means and provided with brushes, and transformer means having its secondary connected to said brushes whereby said commutator and brushes constitute means for supplying direct current to the field winding means when said rotor is at synchronous speed and whereby said rectifier means converts line frequency to the frequency induced in said field winding means during starting and acceleration prior to the time that said rotor attains synchronous speed, said r transformer means having a polyphase series and potential primary, said transformer means having its secondary and primary windings arranged for relative adjustment.

3. A self-compensating synchronous motor comprising two elements consisting of a stator and a rotor, one of said elements being provided with a polyphase winding and the other of said elements being provided with field winding means, synchronous rectifier means driven from said rotor and having segments connected to the field Winding means and provided with brushes, and transformer means having its secondary connected to said brushes, whereby said commutator and brushes constitute means for supplying direct current to the field winding means when said rotor is at synchronous speed and whereby said rectifier means converts line frequency to the frequency induced in said field winding means during starting and acceleration prior to the time that said rotor attains synchronous speed, said transformer means having a polyphase series and potential primary, said transformer means having its secondary and primary windings arranged for relative adjustment, and at least one of said primary windings being adjustable with reference to the other of said primary windings.

4. A self-compensating synchronous motor comprising a stator having a polyphase stator winding and rotor having a squirrel cage and a direct current winding, a secondary winding wound on said stator in transformer relation to the stator winding, a transformer having a secondary winding and a series primary winding, the secondary windings being connected together, and synchronous rectifier means driven from said rotor and connected to said secondaries and to said direct current field winding for supplying direct current to said field winding, the said secondaries having their voltages vectorially added, whereby the shift in the phase angle of the current supplied said direct current field winding corresponds to the torque shift of said synchronous motor thereby resulting in commutation at substantially zero potential irrespective of load conditions imposed on said motor.

5. A self-compensating synchronous motor comprising a stator havin a polyphase winding and a rotor having a squirrel cage and a direct current winding, synchronous rectifier means driven from said rotor for supplying said field winding with direct current, and transformer means having a polyphase primary consisting of two parts, one of which is a series primary and the other of which is a potential'primary and having a polyphase secondary connected to said synchronous rectifier for supplying direct current through said synchronous rectifier to the direct current field winding of said rotor, the polyphase secondary winding havin a plurality of windings having their voltage vectorially added, whereby the shift in the phase angle of the current supplied said direct current field Winding increases with increasing load imposed on the said synchronous motor.

6. A self-compensating synchronous motor comprising a stator having a stator winding, a rotor having two direct current field windings arranged electrically at right angles to each other,

a series transformer having a primary connected in series with the stator win-dings and having secondary winding means, a first synchronous rectifier having segments connected to one of said direct current windings and having brushes connected to the secondary winding'means of said series transformer, a second transformer consisting of a potential transformer having a primary connected in shun-t to said stator winding and having secondary winding means, and a second synchronous rectifier having segments connected to the second direct current field winding of said rotor and having brushes bearing on said segments and connected to the secondary winding means of said second transformer.

KLAUS L. HANSEN.

REFERENCES CITED UNITED STATES PATENTS Name Date Swanson Feb. 14, 1939 Number 

